The present invention relates to functional foods and beverages containing an algin such as alginic acid or an alginate salt or ester which functions as dietary fibers. More particularly, the invention relates to algin-containing health foods and especially beverages, in which the algin has a decreased molecular weight while still retaining its functions as a dietary fiber. Such algin-containing foods have a preventive effect on obesity and diabetes.
Alginic acid is a high molecular weight, polyuronide-type polysaccharide which comprises D-mannuronic acid (abbreviated as M) and L-guluronic acid (abbreviated as G) combined in a varying proportion. It is present between cells of brown algae. The molar ratio of M to G (M/G ratio) of alginic acid varies depending on the species of the alga, season, and location in the algal body.
Alginic acid is made by extracting brown algae such as giant kelp (Macrocystis pyrifera) with an aqueous sodium carbonate solution followed by precipitation with hydrochloric acid or calcium chloride. Free alginic acid is very slightly soluble in water and tends to gel therein. Therefore, in practical use, a water-soluble salt of alginic acid, e.g., an alginate salt with an alkali metal such as sodium is used in the form of an aqueous solution. An aqueous solution of a water-soluble alginate salt is extremely viscous and finds many applications, including as sizing agents, food additives, and paint thickeners.
The term "algin" used herein encompasses alginic acid and its derivatives including alginate salts and esters.
Algin is known to have many desirable effects on human health. When an alginate salt is ingested, it is converted into free alginic acid by a reaction with the acid in the stomach and gelled. The gelled alginic acid cannot be absorbed by humans since mammals have no enzymes capable of digesting alginic acid. Therefore, algin functions as a dietary fiber and is effective in intestinal regulation and prevention of constipation. Sodium alginate is reported to be effective, when administered, in accelerating the excretion of cholesterol and depressing the biological absorption of harmful metals such as strontium and cadmium. An aqueous 5% solution of sodium alginate is clinically used as a drug in treatment of peptic ulcers and esophagitis. Potassium and calcium alginates are reported to have a sodium-excreting activity [see, the Japanese journal "Shokuhin Kaihatsu (Food Development)", Vol. 20, No. 3, pp. 20-23 (1985)].
In Japan, alginic acid, sodium alginate, and alginic acid propylene glycol ester are approved as food additives, while in many European countries and the U.S.A., potassium alginate, ammonium alginate, and calcium alginate are also approved. Thus, many species of algin have been proved to be harmless to the human body.
On the basis of these advantageous effects of algin on health, a health beverage containing alginic acid or sodium alginate has been proposed in Japanese Patent Application Laid-Open (Kokai) No. 55-28956(1980). Japanese Patent Application Laid-Open (Kokai) No. 1-240175(1989) discloses a high-fiber content beverage which comprises water-insoluble dietary fibers dispersed in an aqueous dispersion medium containing a gelling agent and a thickener. It is described therein that alginic acid and its derivatives can be used as a gelling agent. This laid-open application teaches that algin can be merely used as a gelling agent to thicken the beverage without the use of its function as a dietary fiber.
When an alginate salt such as sodium alginate is added to a beverage, it is not possible to increase its content beyond a few percent, because a higher content causes the resulting solution to have an extremely high viscosity which makes the solution no longer suitable for drinking. Therefore, an alginate salt can be used only in the form of a dilute solution having a concentration of a few percent or lower even in beverages as health foods. However, an algin-containing beverage having such a low content cannot achieve the desirable effects of algin.